EP0677749A2 - Abnormality detection method, abnormality detection apparatus, and power generating system using the same - Google Patents

Abstract

It is an object of the invention to accurately detect a defective photoelectric conversion element regardless of the installation place and notify the corresponding information. The above object can be achieved by a power generating system having a solar cell array constituted by a plurality of parallel-connected solar cell strings each consisting of a plurality of series-connected solar cell modules The system includes electrical parameter detection units for measuring electrical parameters in solar cell strings, a comparing unit for comparing the detected electrical parameters mutually, and a warning unit for warning an abnormality on the basis of the comparison result. <IMAGE>

Description

BACKGROUND OF THE INVENTIONField of the Invention
• The present invention relates to a method of detecting an abnormality in a photoelectric conversion element, an abnormality detection apparatus, and a system using the same and, more particularly, to a method and apparatus for detecting an abnormality without using a photoelectric conversion element serving as a standard, and a power generating system using the same.
Related Background Art
• In connection with global warming owing to emission of CO₂ and the like arising from the use of fossil fuels, and radioactive contamination caused by accidents in nuclear power plants and radioactive wastes, the earth environment and energy problems have rapidly become matters of great concern. Under the circumstances, a solar cell as a photoelectric conversion element using incident light is expected worldwide as an inexhaustible, clean energy source. Solar light power generating systems using this solar cell vary in type and scale, ranging from several W to several thousand kW, e.g., a system designed to preserve power generating energy of a solar cell by using a battery, and a system designed to supply output energy from a solar cell to a commercial use system by using a DC-AC converter.
• Fig. 13 shows such a system as a comparative example of the present invention. In this solar light power generating system, asolar cell array 1 is constituted by four parallel-connectedsolar cell strings 11, 12, 13, and 14 each consisting of a plurality of series-connected solar cell modules. An output from thesolar cell array 1 is sent to apower conversion unit 2 including a control unit for performing maximum output control and supplied to aload 3. In this case, theload 3 is an electric power system (e.g., the above commercial use system). A system for supplying electric power from a solar cell to an electric power system is especially called a system interconnection system, which is one of the optimal system forms using a solar cell as a general energy source.
• In general, a solar light power generating system of this type includes various protection units for preventing electrical shocks and the like. However, not many efforts have been made to develop methods of detecting defects in solar cell modules. As such a defect detection method, the following conventional method has been employed. In this method, the conversion efficiency of a solar cell array is calculated by using, e.g., an expensive pyrheliometer and a power measurement unit, and an abnormality in the solar cell array is determined when the conversion efficiency is below a standard value.
• In the above conventional method of detecting a defect in a solar cell module, a standard value for the conversion efficiency is fixed but cannot be properly set in accordance with the climate at a place where each solar cell module is installed, an installed state, and the like. That is, since a solar cell has spectrum or temperature dependency, the conversion efficiency considerably varies. In addition, especially in a solar cell consisting of an amorphous silicon material, the photoelectric conversion element itself undergoes optical deterioration. This deterioration state is greatly dependent on environmental factors such as solar radiation amount and temperature. Therefore, it is very difficult to obtain an accurate standard value upon consideration of these factors, the characteristics of each solar cell, and the like.
• As a means for accurately determining a standard value, only a means of setting a measurement site at the installation place and checking the power generation performance at the corresponding area or the installation place is available. This, however, requires enormous cost and time. In order to solve this problem, a standard module may be installed independently of the solar cell array. However, it is irrational to install a solar cell which does not contribute to power generation. In addition, if the standard module breaks down owing to the influence of a failure or the like of the system, no means of obtaining an accurate standard value is left. Furthermore, a measurement error may occur between the solar cell array for power generation and the module for a standard value.
• In the above method, it is determined on the basis of a standard value whether the overall solar cell array is defective. Even if, therefore, an abnormality is determined, a cumbersome operation is required to find a specific defective part of the solar cell array. For this reason, it takes much time and labor to repair a solar cell array or replace modules.
SUMMARY OF THE INVENTION
• The present invention has been made in consideration of the above situation, and has as its object to provide an abnormality detection method, an abnormality detection apparatus, and a power generating system using the same, which can accurately detect a defect in a solar cell array regardless of the installation place and warn of the abnormality.
• In order to achieve the above object, according to the present invention, there is provided an abnormality detection method comprising the step of detecting electrical parameters in not less than two photoelectric conversion elements, the step of comparing the detected electrical parameters mutually; and the step of detecting an abnormality in the photoelectric conversion elements in accordance with the comparison result.
• In addition, there is provided an abnormality detection apparatus comprising not less than two photoelectric conversion elements, electrical parameter detection means for detecting electrical parameters in the respective photoelectric conversion elements, and comparing means for comparing the detected electrical parameters mutually and detecting an abnormality in accordance with the comparison result.
• Furthermore, there is provided a power generating system including not less than two photoelectric conversion elements, power conversion means for converting electric power from the photoelectric conversion elements, and a load connected to the power conversion means, comprising comparing means for detecting electrical parameters in the photoelectric conversion elements through electrical parameter detection means, and comparing the detection values mutually, thereby detecting an abnormality.
• According to the present invention, electrical parameters, e.g., currents, in the solar cell strings or sub-arrays of a solar cell array during the operation of the system are detected by current sensors as current detection means, and the detected parameters are compared mutually. If any solar cell string or sub-array as a photoelectric conversion element exhibits a relatively low output, an abnormality is determined, and a warning or the like is generated. Alternatively, the variation ratios of the above electrical parameters are compared mutually. If any solar cell, solar cell string, or sub-array exhibits a relatively large variation ratio, an abnormality is determined, and a warning or the like is generated. Such determination is performed by using part of the solar cell array, and an accurate standard value can be determined for each installation place by comparing electrical parameters mutually. Therefore, a defective portion of a solar cell, solar cell string, or sub-array can be accurately detected.
• In addition, since an abnormality can be determined in units of solar cell strings or sub-arrays, a defective portion of the solar cell array can be quickly specified. This effect is conspicuous especially in a system using amorphous solar cells or resin-encapsulated solar cell modules which deteriorate upon exposure to light.
• Furthermore, in a system designed to record electrical parameters, calculate the variation ratios of the recorded electrical parameters, and compare the variation ratios mutually, variations in output over a long period of time are calculated as variation ratios, and the variation ratios can be compared mutually. Therefore, a defective string can be detected in an early stage, and an abnormality can be quickly detected.
• A number of embodiments of the invention will now be described, by way of example only, with reference to the accompanying drawings in which:
• Fig. 1 is a block diagram showing an embodiment of a power generating system according to the present invention;
• Fig. 2 is a flow chart showing the operation of the system in Fig. 1;
• Fig. 3 is a block diagram showing another embodiment of a power generating system according to the present invention;
• Fig. 4 is a flow chart showing the operation of the system in Fig. 3;
• Fig. 5 is a block diagram showing still another embodiment of power generating system according to the present invention;
• Fig. 6 is a flow chart showing the operation of the system in Fig. 5;
• Fig. 7 is a block diagram showing still another embodiment of a power generating system according to the present invention;
• Fig. 8 is a flow chart showing the operation of the system in Fig. 7;
• Fig. 9 is a block diagram showing still another embodiment of a power generating system according to the present invention;
• Fig. 10 is a flow chart showing the operation of the system in Fig. 9;
• Figs. 11A and 11B are graphs showing examples of data for explaining the operation of each embodiment of the present invention; and
• Fig. 12 is a graph showing another example of data for explaining the operation of an embodiment of the present invention; and
• Fig. 13 is a block diagram showing a solar light power generating system for comparison with the present invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
• The present invention will be described in detail below with standard to the accompanying drawings.
• Fig. 1 shows a power generating system using an abnormality detection apparatus according to the present invention. Referring to Fig. 1, asolar cell array 1 comprises parallel-connectedsolar cell strings 11 to 14 each constituted by a plurality of series-connected solar cell modules (which may be simply referred to as modules hereinafter). As a solar cell module, a module using an amorphous silicon (including small crystals), polycrystalline silicon, or crystalline silicon material for a photoelectric conversion unit is preferably used. The number of solar cell modules connected in series may be properly set to obtain a necessary voltage used in the solar light generating system. Generally, in Japan, this number is preferably set to obtain 200 V in a system having an output of 3 kW for household applications; and about 300 to 350 V in a large-scale system having an output of 10 kW or more.
• The number of solar cell string connected in parallel must be at least two or more to achieve the object of the present invention. More preferably, several to several hundred parallel circuits are used. That is, in the present invention, the standard value for a defect dynamically changes in accordance with current parameters in solar cell strings or sub-arrays or variation ratios. If, therefore, the number of strings or sub-arrays is small, a proper standard value is difficult to set. This makes it difficult to perform accurate defect detection. For this reason, the number of parallel circuits is preferably three or more, and more preferably, five or more. As the number of strings or sub-arrays increases, an abnormality can be detected more accurately. However, the number of times of comparison greatly increases to require a cumbersome process, unless some comparing method is devised. In addition, the apparatus cost increases. For this reason, the number of strings or sub-arrays is preferably set to be 100 or less, and more preferably, 30 or less.
Power Conversion Unit 2
• In the abnormality detection apparatus shown in Fig. 1, an output from thesolar cell array 1 is sent to apower conversion unit 2. Thepower conversion unit 2 converts DC electric power from the solar cells into AC electric power or adjusts the DC voltage or the DC current. Thepower conversion unit 2 may include a control system for maintaining the operating point of each solar cell at the maximum output. Although such a unit is not a constituent element of the present invention, the unit is generally used in a system of a several kW class to effectively use the solar cell output. In addition to or in place of this power conversion unit, the system may be designed to directly use secondary batteries. An output from thepower conversion unit 2 is consumed by aload 3.
Load 3
• Theload 3 includes a power-driven device such a motor, a light source such as a lamp, or a heat source such as a laser. More specifically, an air conditioner or the like as anindoor load 31 is exemplified. Alternatively, a storage battery such as a secondary nickel-hydrogen battery, a secondary lithium battery, or a secondary lithium ion battery, acommercial use system 31, or a combination thereof may be used as theload 3.
ElectricalParameter Detection Units 41, 42, 43, 44, 91, 92, 93, and 94
• Electricalparameter detection units 41, 42, 43, and 44 are respectively connected to the solar cell strings 11 to 14. In this case, the electrical parameters may include a voltage, electric power, or a current. A current detection unit is preferably used because the use of a current allows measurements even while the system is in operation. As a detection unit for detecting an electrical parameter, especially a current, a current sensor using a current measurement standard resistor and a Hall element or the like can be used. In detecting a current, the detected current value is converted into a voltage, for example, a current of 10 A is converted into a voltage of 100 mV, and the voltage is output and transmitted to a comparingunit 5. In this case, if the transmission distance to the comparingunit 5 is long, the voltage value may be transmitted via an optical cable by digital transmission or analog transmission using PWM pulse light. With such a transmission method, the influence of noise can be eliminated, and hence a detection signal can be transmitted to a remote location.
• Ifvoltage detection units 91, 92, 93, and 94 are used as electrical parameter detection units, since voltage values can be directly used as parameters, the system arrangement can be simplified.
• When thevoltage detection units 91, 92, 93, and 94 are used as electrical parameter detection units, detection is preferably performed under a small amount (10 mW/cm² or less) of light irradiated on each photoelectric conversion unit for detection.
ComparingUnit 5
• The comparingunit 5 compares transferred detection values mutually. If there is a defective solar cell string having a relatively low output, i.e., a solar cell string exhibiting a value deviated from a group of normal solar cell strings, the comparingunit 5 determines that the solar cell string group has failed, and transmits an output signal to awarning unit 6. In addition, the comparingunit 5 is preferably designed to temporarily store the transmitted data and compare the data mutually. With this arrangement, no specific string is used for a standard value. Therefore, the arrangement is especially effective for solar cells each having output characteristics which sequentially change with time. For such an application purpose, a one-chip microcomputer is very suitable. However, the comparingunit 5 may be constituted by using only analog circuits. If the unit is constituted by only analog circuits, for example, all input values are recorded in a sample/hold circuit, and these values are respectively input to an analog comparator constituted by an operational amplifier so as be compared mutually. Note that comparison values may be switched by an analog switch. In this method, a complicated circuit is required. Therefore, only a first input may be simply used as a standard value. In this case, input values can be sequentially compared mutually, and the circuit can be greatly simplified. Assume that in this method, the first input indicates a failure. Even in this case, if subsequent inputs indicate a normal state, the determination values of the comparing unit shift to the positive side, allowing determination of a non-defective/defective state.
• As the operation mode of the comparingunit 5, a mode of comparison with a rated value, which can be relatively easily realized, or a mode of using a standard deviation or an exponential distribution, which allows accurate detection of an abnormality, can be used.
Warning Unit 6
• As thewarning unit 6, a liquid crystal display such as a TFT or FLC display, a 7 segment LED, a display used for a personal computer, or the like which is capable of character display can be used. That is, this unit can clearly display a specific place where an abnormality has occurred.
• Fig. 3 shows another abnormality detection apparatus for a solar light power generating system which is suitable for the present invention. This apparatus further comprises arecording unit 7 for recording data for a long period of time and allowing the use of the data for maintenance, inspection, and the like, and anarithmetic operation unit 8 for data. With therecording unit 7 and thearithmetic operation unit 8, data from the electricalparameter detection units 41, 42, 43, and 44 can be sequentially processed; This allows the operator to find a faulty solar cell string more quickly.
Recording Unit 7
• As therecording unit 7, a magnetic recording medium such as a floppy disk or a semiconductor memory is used.
Arithmetic Operation Unit 8
• As thearithmetic operation unit 8, a microcomputer is suitably used. In practice, for the sake of convenience, therecording unit 7, thearithmetic operation unit 8, and the like may be integrated with thewarning unit 6 and the comparingunit 5, as shown in Fig. 3.
Communication Unit 61
• As acommunication unit 61, either a wired or wireless communication unit may be used to transmit and notify data based on abnormality detection under centralized control. A modem is used in a telephone line as a wire. Fig. 9 shows only thecommunication unit 61. However, thecommunication unit 61 may also serve as a warning unit.
Correction Unit 81
• In the present invention, it is preferable that light be uniformly incident on the respective strings or arrays to be compared. If, however, it is known in advance that light is incident on the respective strings or arrays at a predetermined ratio of light amounts owing to a certain installation condition, output values from the strings or arrays to be compared may be corrected by thecorrection unit 81 before a comparing operation.
Control Unit 82
• Acontrol unit 82 is constituted by a one-chip microcomputer and the like. Thecontrol unit 82 performs disconnection control on the basis of data from the comparingunit 5 to electrically disconnect a power conversion unit connected to a string in which an abnormality is detected from other power conversion units.
Embodiment 1
• The present invention will be described in detail below in conjunction with an embodiment.
• In this embodiment, as a solar cell module, an amorphous solar cell module (nominal output: 22 W) available from USSC Corp. was used. Ten solar cell strings having an output voltage of about 200 V were formed. Each string was constituted by 14 amorphous solar cell modules connected in series. Wires were extended from these solar cell strings into a house. These wires were connected in parallel to form a solar cell array having an output of 3 kW. As shown in Fig. 1, the output of this solar cell array was connected to apower conversion unit 2. As thepower conversion unit 2, a system interconnection inverter (trade name: Line Back) available from Nihon Denchi K. K. was used. The output of thepower conversion unit 2 was connected to a power system serving as aload 3, thereby forming a system interconnection system having the arrangement shown in Fig. 1.
• Ten current sensors (available from U-RD Corp.; trade name: HCS-20-SC-A-2.5) using Hall elements were used in correspondence with the number of solar cell strings so as to detect string currents in the respective solar cell strings. These current sensors serve to measure currents and convert them into voltages without cutting electric wires. Each sensor used in this embodiment converts a current of 1 A into a voltage of 0.2 V. These current detection-elements were arranged on the string wires in the house. Outputs from the elements were input to a personal computer serving both as a comparing unit and a warning unit via an A/D converter. Data was temporarily recorded by the personal computer. The maximum current among solar cell string currents was defined as 100, and output currents from the remaining solar cell strings were compared with this maximum current. As a current value for comparison, an average value of current values detected every hour from 10 o'clock to 14 o'clock everyday was used for the following reason. In general, in this time zone, since light is uniformly incident on the panel, the solar cell strings can be compared mutually more accurately.
• Fig. 11A shows the initial measurement data of the above measured current values from the respective strings. Similarly, Fig. 11B shows data from the respective strings obtained one year after the above measurement. Referring to Figs. 11A and 11B, the ordinate axis represents the relative current value; and the abscissa axis, the solar cell string number. Determination is performed with standard to these data. Referring to Fig. 11A, solar cell string No. 4 is selected as a standard. Referring to Fig. 11B, solar cell string No. 8 is selected as a standard. As described above, according to the present invention, no specific standard string need be used. Solar cell strings exhibiting relatively good relative current values among measurement data are recognized as a group, and a standard string is properly selected from this group. An output from this standard string can be used as a standard value. Alternatively, an average value of outputs from the solar cell strings may be used as a standard value.
• Referring to Fig. 11B, as is apparent, drops in output have occurred in solar cell strings Nos. 2 and 7. Such a state can be detected, and a warning can be generated. The manager of the system can then take proper measures such as replacement of a solar cell string upon referring to these output drops and the warning. A standard value for determining such output drop may be properly determined for each system (solar cell product). More specifically, since many solar cells exhibit output variations of about 10% in the manufacturing process, a drop of, e.g., about 20% may be considered as a standard.
• As is apparent from the description of this embodiment, the present invention is characterized in that the criterion for determining whether solar cell strings are defective dynamically changes in accordance with the installation location of the system. With this characteristic feature, a defective string can be accurately detected regardless of the installation place or the state of deterioration. The above embodiment exemplifies the case wherein amorphous solar cell modules are used. However, the same effect as described above can be obtained even if crystalline solar cell modules are used in place of amorphous solar cell modules. The operation ofEmbodiment 1 is shown in the flow chart of Fig. 2.
Embodiment 2
• In this embodiment, a system comprises sub-arrays constituting a solar cell array, in place of solar cell strings in the above embodiment. That is, currents are detected in units of sub-arrays, each including the same number of solar cell modules as that in the above embodiment. A defective sub-array is detected by comparing currents measured from the sub-arrays having the same structure, and an abnormality warning is generated.
• With this arrangement, in practice, the defect detection precision slightly deteriorates because of an increase in the number of modules to be monitored by one sensor, but it is apparent that an effect similar to that of the above embodiment can be obtained. If defect detection is performed in units of sub-arrays in this manner, an abnormality detection apparatus according to the present invention can be easily mounted even in a large-scale solar light power generating system of 100 kW or more.
Embodiment 3
• InEmbodiment 3, the arrangement shown in Fig. 3 was realized. A solar cell string having a voltage of 180 V was formed by connecting 12 roof-mount type amorphous solar cell modules (nominal output: 22 W) available from USSC Corp. to each other in series. A solar cell array was constituted by 58 such solar cell strings connected in parallel. A current measurement resistor (0.01 Ω) was used to detect a string current. This detection value was input to a recorder (available from YOKOGAWA ELECTRIC CORP.; trade name: HR2300). An output from the recorder was loaded into a personal computer via a GPIB bus, and the data was recorded in a magnetooptical disk. As described above, in this embodiment, arecording unit 7, anarithmetic operation unit 8, a comparingunit 5, and awarning unit 6 were constituted by the personal computer and the magnetooptical disk, and the integral form shown in Fig. 3 was realized.
• Fig. 12 shows relative performance curves representing the relative comparison results obtained by detecting string currents for 180 days. In this embodiment, a non-defective/defective state of each string is determined, and a defect is detected by using a slope calculation method of calculating the slopes of these relative performance curves at measurement points, i.e., the variation ratios of string currents.
• Referring to Fig. 12, a non-defective string exhibits a slope of 0 as indicated by "Good", whereas a defective string exhibits a negative slope representing a gradual drop in output, as indicated by "Bad". It is known from the research made by the present inventors that variations in deterioration of solar cell strings are smaller than variations (about ±10%) in performance of the solar cell modules under the same environment. Therefore, by checking the slope of a relative performance curve based on each string as in the above slope method, a defective string can be detected at a time point at which the corresponding slope becomes negative, i.e., the time point indicated by "F" in Fig. 12, and a warning can be generated. More specifically, if the relative output measured 10 days before the currently measured output is larger than the current output by 3 to 5%, it is determined that the corresponding string will fail soon. When string currents corresponding to only one day are to be compared mutually, since variations (about ±10%) in performance of the modules are large as described above, a warning cannot be generated till a time point at which a deterioration in performance has advanced to a certain degree, e.g., the time point indicated by "H" in Fig. 12. When long-term data monitoring is performed as in this embodiment, a defect can be detected more quickly, and corresponding measures can be quickly taken. In addition, especially in resin-encapsulated solar cell modules, since current drops sequentially change, a defective solar cell module can be predicted to allow maintenance and inspection.
• As described above, in the present invention, the recording unit and the arithmetic operation unit for detected data are arranged to perform arithmetic processing for electrical parameters so as to obtain variation ratios. If a defect is detected by comparing these variation ratios mutually, a warning can be generated more quickly. In addition, since detected data of electrical parameters are recorded, the cause of a failure can be found by using such data.
• The operation ofEmbodiment 3 is shown in the flow chart of Fig. 4.
Embodiment 4
• Fig. 5 showsEmbodiment 4.
• Avoltage detection unit 9 is used to detect voltages fromstrings 11 to 14 by usingdetection units 91 to 94 in place of the current detection unit used as an electrical parameter detection unit inEmbodiment 1. Asloads 3, acommercial use system 31 and anindoor load 32 are arranged. The arrangement of this embodiment is the same as that ofEmbodiment 1 except for the above points. When thevoltage detection unit 9 is used, measurement must be performed after it is confirmed that the light amount is small, i.e., 10 mW/cm². In addition, in order to eliminate errors due to voltage variations accompanying load variations, measurement is preferably performed while the circuit is in an open state.
• With the above arrangement, the present invention can be realized by a relatively simple apparatus arrangement.
• The operation ofEmbodiment 4 is shown in the flow chart of Fig. 6.
Embodiment 5
• Fig. 7 showsEmbodiment 5. The arrangement of this embodiment is the same as that ofEmbodiment 1 except that a solar cell array is divided into two arrays. These two solar cell arrays are arranged at positions where the amounts of incident light are different, and the data of current detection values from the respective arrays are corrected by a correction unit. Thereafter, the data are compared mutually.
• Current detection values from the respective solar cell arrays are compared when they are installed, and correction values are set in the correction unit on the basis of the resultant value.
• With this arrangement, the solar cell arrays can be installed at different angles in the same place at which the amounts of incident light are different.
• The operation ofEmbodiment 5 is shown in the flow chart of Fig. 8.
Embodiment 6
• Fig. 9 showsEmbodiment 6.
• Power conversion is performed by each power conversion unit for each string. The resultant values are then detected by electricalparameter detection units 41 to 44, respectively. The respective strings are compared mutually by a comparingunit 5.
• If an abnormality is found among the strings, acontrol unit 82 stops a power conversion unit for the corresponding string. At the same time, the corresponding information is displayed on a display at a distant place by acommunication unit 61 via a wire. With this arrangement, only an abnormal string can be disconnected from the power generating system, and at the same time, a warning about the abnormality can be generated.
• The operation ofEmbodiment 6 is shown in Fig. 10. As described above, according to the present invention, the following effects can be obtained.
• (1) An accurate standard value can be determined in each installation place and updated as time elapses so that defective portions of sub-arrays and solar cell strings as photoelectric conversion elements can be accurately detected. Especially in an amorphous solar cell, the state of deterioration changes depending on the installation place and the use history. If, therefore, the criterion for determining a non-defective/defective state can be changed in accordance with the state of deterioration as in the present invention, a defective portion can be detected in consideration of the state of deterioration. Similarly, the present invention is effective for resin-encapsulated photoelectric conversion elements because the characteristics of each element change over time.
• (2) By recording electrical parameters as data and checking changes in the recorded data with time, an abnormality warning can be quickly generated, and centralized control of a plurality of strings can be performed by using a communication unit. Therefore, a defective portion can be replaced before a fatal failure, e.g., a considerable drop in output, occurs.
  In addition, data recording contributes to a thorough search for the cause of a failure.
• As has been described above, the present invention is very effective for preventive maintenance of a power generating system, and is especially effective for a large-scale solar light power generating system. Furthermore, such a warning unit is incorporated in a control unit for a power conversion unit so that the system can be operated by using only non-defective portions while a defective portion is disconnected therefrom. Therefore, the reliability of the system can be improved.

Claims (49)

1. An abnormality detection method comprising the step of detecting electrical parameters in not less than two photoelectric conversion elements, the step of comparing the detected electrical parameters mutually; and the step of detecting an abnormality in said photoelectric conversion elements in accordance with the comparison result.
2. A method according to claim 1, wherein said photoelectric conversion element is a solar cell module obtained by connecting solar cells in series and/or in parallel.
3. A method according to claim 2, wherein said photoelectric conversion element is a solar cell string obtained by connecting solar cell modules in series and/or in parallel.
4. A method according to claim 3, wherein said photoelectric conversion element is a solar cell sub-array obtained by connecting solar cell strings in series and/or in parallel.
5. A method according to claim 4, wherein said photoelectric conversion element is a solar cell array obtained by connecting solar cell sub-arrays in series and/or in parallel.
6. A method according to claim 1, wherein said photoelectric conversion element is a non-monocrystalline semiconductor.
7. A method according to claim 6, wherein said non-monocrystalline semiconductor is an amorphous semiconductor.
8. A method according to claim 6, wherein said non-crystalline semiconductor is resin-encapsulated.
9. A method according to claim 1, wherein the electrical parameter is a current.
10. A method according to claim 1, wherein the electrical parameter is a voltage.
11. A method according to claim 1, wherein an electrical parameter is detected during an operation of said photoelectric conversion element.
12. A method according to claim 1, wherein said photoelectric conversion element is operated and the electrical parameter is detected when irradiated light energy is not more than 10 mW/cm².
13. A method according to claim 1, wherein the step of comparing the electrical parameters comprises the step of recording the electrical parameters, the step of calculating variation ratios on the basis of the recorded values, and the step of comparing the electrical parameters on the basis of the variation ratios.
14. An abnormality detection apparatus comprising not less than two photoelectric conversion elements, electrical parameter detection means for detecting electrical parameters in said respective photoelectric conversion elements, and comparing means for comparing the detected electrical parameters mutually and detecting an abnormality in accordance with the comparison result.
15. An apparatus according to claim 14, wherein said photoelectric conversion element is a solar cell module obtained by connecting solar cells in series and/or in parallel.
16. An apparatus according to claim 15, wherein said photoelectric conversion element is a solar cell string obtained by connecting solar cell modules in series and/or in parallel.
17. An apparatus according to claim 16, wherein said photoelectric conversion element is a solar cell sub-array obtained by connecting solar cell strings in series and/or in parallel.
18. An apparatus according to claim 17, wherein said photoelectric conversion element is a solar cell array obtained by connecting solar cell sub-arrays in series and/or in parallel.
19. An apparatus according to claim 14, wherein said photoelectric conversion element is a non-monocrystalline semiconductor.
20. An apparatus according to claim 19, wherein said non-monocrystalline semiconductor is an amorphous semiconductor.
21. An apparatus according to claim 14, wherein said non-crystalline semiconductor is resin-encapsulated.
22. An apparatus according to claim 14, wherein said electrical parameter detection means is current detection means.
23. An apparatus according to claim 14, wherein said electrical parameter detection means is voltage detection means.
24. An apparatus according to claim 14, wherein an electrical parameter is detected during an operation of said photoelectric conversion element.
25. An apparatus according to claim 14, wherein said photoelectric conversion element is operated and the electrical parameter is detected when irradiated light energy is not more than 10 mW/cm².
26. An apparatus according to claim 14, wherein said comparing means is connected to recording means for recording electrical parameters and arithmetic operation means for calculating variation ratios on the basis of values recorded by said recording means so as to detect an abnormality on the basis of the variation ratios calculated by said arithmetic operation means.
27. An apparatus according to claim 14, wherein the abnormality is displayed by warning means.
28. An apparatus according to claim 14, wherein the abnormality is transmitted by communication means.
29. A power generating system including not less than two photoelectric conversion elements, power conversion means for converting electric power from said photoelectric conversion elements, and a load connected to said power conversion means, comprising
       comparing means for detecting electrical parameters in said photoelectric conversion elements through electrical parameter detection means, and comparing the detection values mutually, thereby detecting an abnormality.
30. A system according to claim 29, wherein said photoelectric conversion element is a solar cell module obtained by connecting solar cells in series and/or in parallel.
31. A system according to claim 30, wherein said photoelectric conversion element is a solar cell string obtained by connecting solar cell modules in series and/or in parallel.
32. A system according to claim 31, wherein said photoelectric conversion element is a solar cell sub-array obtained by connecting solar cell strings in series and/or in parallel.
33. A system according to claim 32, wherein said photoelectric conversion element is a solar cell array obtained by connecting solar cell sub-arrays in series and/or in parallel.
34. A system according to claim 29, wherein said photoelectric conversion element is a non-monocrystalline semiconductor.
35. A system according to claim 34, wherein said non-monocrystalline semiconductor is an amorphous semiconductor.
36. A system according to claim 29, wherein said non-crystalline semiconductor is resin-encapsulated.
37. A system according to claim 29, wherein said electrical parameter detection means is current detection means.
38. A system according to claim 29, wherein said electrical parameter detection means is voltage detection means.
39. A system according to claim 29, wherein an electrical parameter is detected during an operation of said photoelectric conversion element.
40. A system according to claim 29, wherein said photoelectric conversion element is operated and the electrical parameter is detected when irradiated light energy is not more than 10 mW/cm².
41. A system according to claim 29, wherein said power conversion means is a DC-DC converter.
42. A system according to claim 29, wherein said power conversion means is a DC-AC converter.
43. A system according to claim 29, wherein said load is a power system.
44. A system according to claim 29, wherein said load is storage battery means.
45. A system according to claim 29, wherein an operation of said power conversion means is controlled by control means connected to said comparing means which has detected the abnormality.
46. A system according to claim 29, wherein said power conversion means are arranged in correspondence with said photoelectric conversion elements.
47. An apparatus according to claim 29, wherein said comparing means is connected to recording means for recording electrical parameters and arithmetic operation means for calculating variation ratios on the basis of values recorded by said recording means so as to detect an abnormality on the basis of the variation ratios calculated by said arithmetic operation means.
48. An apparatus according to claim 29, wherein the abnormality is displayed by warning means.
49. An apparatus according to claim 29, wherein the abnormality is transmitted by communication means.

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